Quaternary ammonium hydroxides in aqueous solution are quite stable. However, quaternary ammonium hydroxides in non-aqueous solvents tend to develop undesirable coloration on standing or storage, even at room temperature, but particularly at elevated temperatures. Although not to be bound by theory, it is considered that one reason for the color development is a Hoffman elimination of a propyl or higher length alkyl substituent of the quaternary ammonium compound, to form an alkene that subsequently reacts to form a colored compound. For example, the following reaction may take place, yielding an alkene that could polymerize or otherwise react to form a colored compound in the quaternary ammonium non-aqueous solution:
The development of color in a quaternary ammonium compound in a non-aqueous solvent is undesirable for a number of reasons, but has been a long-standing problem that has proven difficult to solve. One solution has been to add formaldehyde to the non-aqueous quaternary ammonium solution, but it is well known that formaldehyde is undesirable in many systems.
Thus, the tendency of quaternary ammonium hydroxides in non-aqueous solvents to develop undesirable coloration on standing or storage has resisted solution and there has been a long-standing need for a solution to this problem.